1. Field of the Invention
The present invention relates to a sheet feeding apparatus, and more particularly, it relates to a sheet feeding apparatus for feeding a sheet in a printing portion of a printer and the like.
For example, a printer to which the present invention is applied may be a printer of so-called BJ scan type, wherein after the printing of a line having a predetermined width is effected, an auxiliary scanning is performed by a next predetermined width and a next line is printed, thereby forming an image.
2. Related Background Art
In the past, various printers having heat-sensitive features heat transfer features or ink jet features have been put to practical use. Among them, in an ink jet printer wherein an image is printed on a sheet by discharging liquid, since the sheet was stretched during the printing operation, a counter-measure to the stretching of the sheet was required for performing the accurate feeding of the sheet. That is to say, in the past, a feeding amount of the sheet was controlled by gripper rollers gripping or pinching a non-stretched portion of the sheet (i.e., a portion of the sheet on which an image has not yet been printed), and contact rollers contacting with a printed portion of the sheet were rotated faster than the gripper rollers (for example, by about 5%), thus ejecting the sheet while slipping the contact rollers on the sheet.
Now, when the image is tried to be printed on the whole surface of the sheet having a regular size by shifting a head in a main scanning direction (perpendicular to a plane of FIG. 1), as shown in FIG. 2, since, while the sheet is being fed by the gripper rollers, an auxiliary scanning feed of the sheet is effected by a distance L.sub.1 corresponding to a printing width of one line every printing operation, a printed line is correctly contiguous to the previous printed line, thus obtaining the image having no discontinuity. However, when the sheet leaves the gripper rollers, since the sheet is fed only by the faster contact rollers contacting the printed portion of the sheet, the auxiliary scanning feed of the sheet will be effected by a distance L.sub.3 longer than the distance L.sub.1. Consequently, the printed lines are not contiguous to each other, thus creating a blank area corresponding to a width (L.sub.3 -L.sub.1) in the image.
To avoid this, a sheet having a length sufficiently greater than a printing area was used conventionally.